Transistors, such as n-channel field effect transistors (NFET) and p-channel field effect transistors (PFET), formed in a complementary-metal-oxide silicon (CMOS) integrated circuit, operate when an input voltage is applied to a gate voltage. This gate voltage establishes an electric field perpendicular to a channel between a source and drain of the transistor. A conductance of the channel is controlled by the electric field. If no gate voltage is applied, a path between the source and drain is formed as two back-to-back p-n junctions, and the drain current is negligible. When a positive voltage is applied to the gate of the transistor, electrons are attracted to the channel. When the gate voltage exceeds a threshold level, an inversion layer is formed in the channel to couple the source and drain. The threshold voltage level of a transistor is dependent on several variables, both controllable and uncontrollable.
In order to save power when not in use, CMOS transistors are typically transitioned to a standby mode to reduce their power consumption. Fast switching (or wake-up) of the transistors from standby mode to active mode is a goal for processing efficiency. External power and high-speed charge circuits are typically implemented to improve switching speed from standby mode to active mode.